Method of detecting a frame synchronization pattern or unique word in a received digital signal

Abstract

The recognition of a frame synchronization pattern or unique word of a received signal may be enhanced using a data-aided estimator of the signal-to-noise ratio (SNR) together with a correlation detector of the unique word to be received. Detecting a frame synchronization pattern or a unique word in a received signal, the SNR is estimated on the received signal with a data-aided SNR estimator using the unique word to be received. If the estimated SNR exceeds a certain threshold, an eventual recognition of the unique word established by a correlation correlator of the receiver is considered reliable. Comparing the SNR with the threshold may be carried out either before or after the correlator has processed the unique word.

Description

FIELD OF THE INVENTION[0001]The invention relates to communication systems, and, more particularly, to a method of detecting a frame synchronization pattern or unique word in a received signal.BACKGROUND OF THE INVENTION[0002]Throughout this document the term “frame” will denote the sequence of symbols that includes the useful part of the transmitted data. To correctly demodulate a received signal, a receiver must recognize the beginning of the useful part. Typically, the transmitter inserts before the data bits two pre-determined bit-sequences referred as “preamble” and “unique word” (UW). The preamble sequence is mainly used for symbol, clock synchronization or carrier recovery purposes, while the UW is used to obtain frame synchronization.[0003]Recognition or detection of a known sequence of bits contained in the received stream is generally carried out via a correlator. Typically, the correlator is hard input based, although also soft input based correlator approaches exist. In ...

AI Technical Summary

Benefits of technology

[0010]It has been found that the recognition of a frame synchronization pattern or unique word of a received signal may be enhanced using a data-aided estimator of the signal-to-noise ratio (SNR) together with a correlation detector of the unique word to be received. Incorrect recognitions of the unique word in the received signal by the correlation detector occur substantially when noise pulses of the transmission channel match partially with the true UW and so may be erroneously recognized as pulses of the unique word.

Problems solved by technology

A problem of such a scheme is that if the chosen correlation threshold is too high, i.e. if a large number of matches is required between the pre-stored UW and the received signal, the probability of missed detection in the presence of noise is high.

Conversely, if the correlation threshold is too low, the probability of false detection grows and false alarms are generated with high frequency.

These approaches do not completely address the problem of limiting the missed and false UW detections.

By checking the presence of more than one UW, also the false detections are limited.

Moreover, the repetition of the same UW sequence, instead of increasing the UW length, limits the dimension of the correlator at the receiver.

However, the achievements of this technique are obtained at the cost of a transmission overhead that may be undesirable in many applications.

Besides the problem of the introduced redundancy, a drawback of this method is the need of coding the UW.

This procedure does not avoid false detections during the first frame UW acquisition or implies an acquisition delay for verifying whether other UWs follow.

This approach reduces false detections, since the correlator is switched off for a very long time.

Moreover, the received signal power is not directly linked to the system performance, which determines the missed detection probability, thus, the threshold setup is not simple.

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